Brush shunt connections



Nov. 13, 1962 s. RUSYNYK BRUSH SHUNT CONNECTIONS Filed Oct. 28, 1959 e r u l VA h M Wk nw M le aln DI C- w m0 p ME Copper Shunr INVENTOR. SAMUEL RUSYNYK LQMWM ATTORNEY 3,064,151 BRUSH SHUNT CONNECTIONS Samuel Rusynyk, Parma, Ohio, assignor to Union Carbide Corporation, a corporation of New York Filed Oct. 28, 1959, Ser. No. 849,407 2 Claims. (Cl. 310-249) This invention is concerned generally with electrical contact brushes for use in sliding contact with commutators or contact rings of electrical machinery. More specifically, the invention is concerned with an improved doping mixture for tamped brush shunt connections.

Most electrical contact brushes are fabricated from carbon or graphite, often in admixture with a metal, usually copper. When used in conjunction with commutators or contact rings of electrical machinery, they are held in contact by a holder and spring which permits some motion of the brush to accommodate any unevenness in commutator or ring surface, and to maintain constant contact as the brush is shortened by wear. To conduct the electrical current to or from the brush, a flexible Wire or cable shunt is fastened to an end of the brush either by a rivet, a bolt, or by inserting an end of the shunt into a preformed hole in the brush and fastening it thereto by means of a conductive cement or tamped metal powder or amalgam. The last named fastening means is referred to as a tamped connection.

It has been known for some time by those skilled in the art that almost any conductive metal powder such as copper powder can be tamped in tamped connections so that the initial electrical and mechanical characteristics of the brush connection seemingly indicate a desirable, stable connection. However, as the tamped connections age, or as they are subjected to comparatively small increases in temperature, oxidation of the metal takes place. As a result, the connection resistance rises as much as 400 percent. This increase in connection resistance is prohibitive, so far as the efficient operation of most electric contact brushes is concerned.

The main object of this invention then is to provide means for protecting tamped shunt connections from oxidation.

Another object of this invention is to provide a novel doping composition which can readilv be applied to tamped copper powder brush shunt connections to protect the same against oxidation.

Still another object of the invention is to provide a brush shunt connection having a relatively uniform resistance.

A further object of the invention is to reduce the tendency of brush shunt connections to undergo mechanical failure resulting from a shake-out of the tamped metallic powder.

The invention whereby the foregoing objects are attained comprises an electrical contact brush fabricated from graphite or carbon, or mixtures thereof with a metal, and having a shunt cable secured by tamped metal in a cavity in the brush body, the tamped metal having a coating of a doping mixture of phenolic and epoxy resins.

The accompanying single FIGURE of the drawing shows a partially cut-away view of a brush made in accord with the invention.

The doping mixture used in this invention comprises from to 80 percent by weight of phenolic resin, the balance an epoxy resin. The mixture is diluted with from 40 to 70 percent by weight thereof of acetone. The resulting range of specific gravity of the mixture varies from 1.050 at 40 percent dilution to 0.925 at 70 percent dilution, at C. These compositions are quite mobile, and penetrate completely the tamped material.

The preferred formulation of the epoxy phenolic dope is percent by weight of a phenol formaldehyde resin in the B stage which resin acts as the hardener for the formulation and 20 percent byweight of epoxy resins such as the diglycidyl ether of bisphenol A. 'Bisphenol A is the commonly used term to denote bis (4hydroxyphenyl) demethylmethane. Sixty percent by weight of the mixture of acetone is added to give a final specific gravity of 0.933 at 25 C. The curing time of the mixture is two hours at C.

In the practice of the invention, after the brush cable connection is formed conventionally, a mixture within the composition range above indicated is applied locally to the tamped metal, as with a dropper. The mixture penetrates the tamped metal and uniformly coats the particles thereof. The mixture is then cured conventionally, as by placing the assembly in an oven. After curing, the mixture acts as a bonding agent, and increases the pullout strength of the connection. The flake copper powder used has a grease content of 0.025 percent maximum, and the following screen analysis:

4.46% on 48 mesh 30.69% on mesh 41.26% on mesh 7.96% on 200 mesh 6.52% on 325 mesh 9.11% through 325 mesh However, the practice of the invention is not limited to the use of flake copper powder, or to the given screen analysis, as copper powder produced by the gas reduction process or by the electrolytic process will also function satisfactorily. In fact, other suitably conductive metals may be substituted for copper.

The relative oxidation prevention elfectiveness of the composition of the invention was investigated by a series of tests. Test data are tabulated in Table 1 below.

TABLE 1 I [Oxidation test at 150 C, Connection resistance (milliohms)] 1 A tung oil base varnish.

The results indicate that the epoxy-phenolic mixture was as much as 100 percent superior to furfuryl alcohol as a means of preventing the oxidation of the tamped copper powder brush shunt connection. The use of an epoxyphenolic doping mixture not only provides a more superior oxidation prevention sealant than has heretofore been available, but it also provides a brush shunt connection having a relatively uniform connection resistance. This table shows also the oxidation resistance superiority of an epoxy-phenolic doped tamped copper powder connection over a furfuryl alcohol doped amalgam connection which has a resilient cement cap for added protection.

Additionally, in an attempt to determine the electrical stability of copper powder tamped connections, a current overload test was made. This test consisted of subjecting the individual connections to currents of 50, 75 and 100 amperes for five-minute periods at each current level. These current levels represent current overloads of from 25 percent to 150 percent, and produced temperatures in the connection area ranging from 150 C. to 450 C After the overload test, connection resistance and mechanical' pullout strength measurements Were made to determine the degree of electrical and mechanical deterioration which occurred. These tests were compared with similar 4 per particles employed in the connection. This results in an oxidation resistant connectionwhich has exceptionally stable electrical and mechanical properties.

' (2) The epoxy-phenolic mixture retains its excellent tests conducted on furfuryl alcohol doped tamped copperwetting and bonding properties at temperatures above that mercury (almalgam) brush shunt connections. The reat which either resin would function satisfactorily if used sults of this comparative test show that the connection realone. sistance of the epoxy-phenolic doped copper powder con- (3) The epoxy-phenolic mixture has excellent metal to nection did not exceed 4:milliohms, whereas the conneccarbon bonding properties as well as metal to metal. tion resistance of the standard furfuryl alcohol doped What is claimed is: amalgam connection exceeded 7 milliohms. The results 1. An electrical contact brush comprising a body and a are reported in Table 2. shunt cable secured by tamped copper powder particles in TABLE 2 v Resistance and Pullout StrengthCwrrent Overloald Test 7 Current Overload Test Resistance After Pullout Strength Connection Material Initial Pullout Initial Resistance Temp., C. 50, 75, 100 Current Overload After Current Strength (Lbs) (Milliohms) Amps. (5 Min.) Test (Milliohms) Ove1lIo%d)'Iest (Tamped Amalgam Furiuryl .Al- '190 1.84 188 0. 294 0. 412 C. 7. 26 125 001101 Dope.) 7 (185-200) (1. 4-2. 4) (1e0-2(%5 2 135-315) (6. 4-8. 5) (120-135) (Tamped Copper Epoxy-Phenolic 200+ 2. 36' 206 0. 293 6. 411 0. 3.23 119 Dope.) (1. 0-2. s) (1802(3%)5 4(22g)5325) (3. 0-3. 4) (110-125) It has also been observed that underconditions of exconnection with an 80 percent phenolic and percent epoxy resinous mixture diluted with 60 percent by weight acetone, this type of premature shake-out was eliminated. In subsequent vibration tests employing epoxy-phenolic 'doped tamped copper powder connections, data indicated that shake-out of the doped copper powder shunt connection did not occur until an excess of 22.0 million vibra- 'tions Were experienced. In fact, most epoxy-phenolic doped copper powder shunt connections outlasted the Hex ural life of the conductive shunt cable.

The advantages obtained by the use of an epoxy-phenolic resin sealing and doping mixture of the invention is believed to be due to the following cogent reasons:

(1) The excellent Wetting characteristics of the epoxyphenolic mixture facilitate the uniform coating of the copa cavity in said body, said body being composed of a material selected from thegroup consisting ofcar bon, graphite and mixtures of metal with said material, each of said tamped copper powder particles having a uniform coating of a'cured mixture of an epoxy and a phenolic resin which comprises from 20 to percent by Weight of said phenolic resin with the balance epoxy resin, to preventthe oxidation of said copper powder particles.

2. The electrical contact brush of clairnl wherein said cured mixture of a phenolic and an epoxy resin comprises 80 percent by weight of phenol formaldehyde resin in the of. a bisphenol A resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,483 Castan July 20, 1943 2,521,911 Greenlee Sept. 12, 1950 2,631,252 Falcettoni Mar. 10, 1953 2,687,396 McLean Aug. 24, 1954 2,779,668 Daniels 'Jan. 29, 1957 2,849,631 

